What happens to your metabolism after 40?

(And why it’s not just about getting older)

If you’ve noticed that your usual approach to food, exercise and self-care no longer works the way it used to, you’re not imagining it.

Many people in their 40s and 50s start to feel as though their body is changing in ways they didn’t expect – and metabolism often feels like the culprit.

But what actually is metabolism? And why does it seem to ‘slow down’ as we get older?

Let’s have a look.

What is metabolism?

Your metabolism is the collection of processes your body uses to turn food into energy. It includes things like digestion, blood sugar regulation, hormone activity and even how your cells repair themselves.

A lot of people think metabolism is just about how fast you burn calories – but really, it’s about how efficiently your body uses energy and keeps everything in balance.

What changes after 40?

From your late 30s onwards, your metabolism may begin to shift – not because something is ‘wrong’, but because your body is adapting.

Here are some of the key changes that can affect how you feel:

1. Hormones start to fluctuate

   
   

   For women, perimenopause (which can start in your 40s and sometimes earlier) brings a drop in hormones oestrogen and progesterone.

   
   

   For men, testosterone may gradually decline.

   
   

   These hormonal shifts can affect appetite, energy use, sleep and even how your body stores fat – particularly around the middle.

2. Muscle mass tends to decrease

   
   

   Muscle is metabolically active tissue – it helps to burn energy even when you're not moving.

   
   

   In fact, muscle burns more calories at rest than fat does, which means that the more muscle you have, the more efficiently your body uses energy overall.

   
   

   But unless you're actively working to maintain it, muscle mass naturally starts to decline with age – especially during and after midlife.

   
   

   Less muscle means a slower resting metabolism, and that can contribute to weight gain, fatigue and blood sugar issues over time.

3. Insulin sensitivity can reduce

   
   

   As we age, the body may become a little less responsive to insulin – the hormone that helps to move sugar out of the blood and into cells.

   
   

   This can lead to higher blood sugar levels, more frequent crashes, and an increased risk of weight gain, cravings and longer term conditions like pre-diabetes and type 2 diabetes.

4. Stress takes a bigger toll

   
   

   People in midlife are juggling more than ever – careers, ageing parents (who may not live close by), children, relationship separations and other big life transitions.

   
   

   This juggling can cause chronic stress (which you may or may not be able to feel).

   
   

   Chronic stress triggers cortisol, which over time can impact blood sugar regulation, sleep quality and fat storage (particularly abdominal fat).

5. Sleep may get disrupted

   
   

   Hormonal shifts, blood sugar imbalances and life stress can all mess with your sleep – and poor sleep makes it harder for your metabolism to function smoothly.

   
   

   It can increase hunger hormones and reduce your ability to regulate food intake.

It’s not your fault – but it is in your power to change

These changes are common, but they don’t mean you’re stuck.

The key is recognising that your body isn’t broken – it’s just different now. It needs a different kind of support.

And that’s where personalised, practical nutrition can make a huge difference.

If you’re feeling tired, stuck or frustrated with your changing body, you’re not alone – and you don’t have to figure it out by yourself.

Ready to understand what’s happening beneath the surface? Let’s talk – I’d love to help.

Contact me

Disclaimer

The information and advice I provided here is of a general nature and should never replace individual health or medical advice provided by your doctor or other healthcare professional involved in your care.